Electronic alarm and emergency voice communication system

ABSTRACT

The present invention relates to a combination electronic alarm and emergency voice communication system which combines a fire alarm module and an emergency voice communication module in a single system and also provides for optional inclusion of one or more general alarm signals, the system being designed to provide predetermined priorities between voice communication signals, fire alarm signals and general alarm signals, and including improved apparatus for interconnecting the various modules and for supervising the same.

United States Patent [191 Gosswiller et al.

[4 1 Sept. 16, 1975 i 1 ELECTRONIC ALARM AND EMERGENCY VOICE COMMUNICATION SYSTEM [75] Inventors: Earl W. Gosswiller, Clarendon Hills;

Dick T. Hsu, Park Forest; Richard H. Williams, Wheeling, all of L; Joel G. lacono, Highland, Ind.

[73] Assignee: Federal Sign and Signal Corporation, Chicago, Ill.

[22] Filed: May 14, I973 [21] Appl. No.: 359,987

[52] U.S. Cl 340/409; 340/216; 340/384 E; 340/4l6; 340/2l7 {51 I Int. Cl. G08b 29/00 [58I Field of Search 340/409, 216, 4l6, 22l, 340/3l l, 224

[56] References Cited UNITED STATES PATENTS 2,479,621 8/1949 Jackson 340/216 2,525.697 lO/l950 Lurie .7 340/224 2,744.]94 5/l956 Auerbach v. .7 340/224 3,487,404 12/1969 Midkifim 340/4l6 3,493,967 2/1970 Ressler v i i l 340/4l6 3,656.]58 4/l972 Goodwater H 340/409 Primary Examiner-Thomas B. Habecker Attorney, Agent, or Firm-Charles F. Pigott, Jr.

[ 5 7 ABSTRACT The present invention relates to a combination electronic alarm and emergency voice communication system which combines a fire alarm module and an emergency voice communication module in a single system and also provides for optional inclusion of one or more general alarm signals. the system being designed to provide predetermined priorities between voice communication signals, fire alarm signals and general alarm signals, and including improved apparatus for interconnecting the various modules and for supervising the same.

18 Claims, 4 Drawing Figures AMPLIFIER ""z ELECTRONIC ALARM AND EMERGENCY VOICE COMMUNICATION SYSTEM BRIEF SUMMARY OF THE INVENTION It is known in the art to combine a fire alarm system with a music or paging system and to provide means for giving priority to the fire alarm system whereby upon initiation of a fire alarm signal the music or paging system is disconnected from a speaker circuit and a fire alarm tone generator is connected thereto. It is also known to provide means in such a system for supervising the fire tone generator and the amplifier and speaker circuits so as to detect malfunctions therein and produce a visual or audible trouble signal when such problems occur.

A known system of the foregoing type is shown in Goodwater U.S. Pat. No. 3,656.158. The latter patent discloses a system comprising a fire tone signal generator, an input from a paging or music system. an oscillator for producing a low level supersonic signal, and an audio circuit which includes an amplifier and speaker network. Under normal conditions the input from the paging or music system is connected with the audio circuit, and the fire tone signal generator is disconnected, the fire tone generator being continuously operable and being connected to a relay for supervisory purposes. Moreover. under such normal conditions, the oscillator is connected with the amplifier and speaker network by a pair of lines which extend from the signal generator module to the remotely located speakers which are connected in parallel. A return supervisory loop extends back to a supervisory relay associated with the signal generator module at a central control station. In this manner. the entire audio circuit including the amplifier network and the speaker network is supervised by a low level supersonic signal produced by an oscillator.

A system of the foregoing type has certain limitations and disadvantages due to the components provided and the manner of interconnecting and supervising the same. In such a system comprising only a single amplifier and fire tone generator, there is the obvious limitation that the system will not function if either such component is inoperative. since there is no provision for an alternate amplifier or fire tone signal generator. Moreover, such a system is designed to combine one amplifier module with a corresponding tone generator module, and there is no provision for utilizing a single tone generator module to power a plurality of remote amplifier modules. Furthermore, use of a supersonic signal to supervise the amplifier and speaker networks has the diadvantage of requiring a vast amount of cable due to the need for a return supervisory loop. i.e., the necessity of having two lines extend from the generator module at a central control station out to all of the remote speakers which may be located throughout a building and then back to the central control station.

It is therefore a general object of the present invention to provide an improved fire alarm and emergency communication system having unique supervisory means which minimizes the amount of cable required for supervising a remote speaker network.

Another object of the invention is to provide a combination system as above-mentioned including a continuously operating fire tone signal generator which under normal conditions is connected to an amplifier circuit for supervisory purposes, together with means which connects the amplifier circuit with a speaker network only during an alarm condition or upon activation of a voice communication module.

A further related object of our invention is to provide a separate d.c. signal source which under normal conditions is connected with a speaker network for supervising the latter and which is disconnected from the speaker network during an alarm condition or upon activation of a voice communication module.

An additional object of the invention is to provide a combined fire alarm and voice communication system including means for disconnecting the fire tone signal generator from the system whenever the voice communication module is activated thereby giving priority to the voice communication portion of the system to assure that the latter can be operated during a fire alarm.

Still another of our objects is to provide a system as last above-mentioned including detector means for detecting the loss of an amplifier output signal during a fire alarm condition or under normal conditions in the absence of an alarm, and means for disabling such detector means whenever the voice communication module is activated.

A further object is to provide a combined fire alarm and voice communication system which permits use of a single signal generator module in combination with a large number of amplifier modules, each amplifier module being used in conjunction with a network of associated speakers.

A still further one of our objects is to provide a combination system as above-mentioned wherein a fire tone signal is utilized to supervise the amplifier circuit and a separate d.c. signal is utilized to supervise the speaker circuit, and wherein each of the speakers is connected with an associated capacitor which isolates the speaker from the do supervisory signal while permitting normal functioning of the speaker when the amplifier circuit is connected thereto during an alarm condition or upon activation of a voice communication module.

An additional object is to provide a combination system as last above-mentioned which permits connection of an auxiliary amplifier to the speaker circuit for music, paging or other auxiliary input without interfering with the normal supervision of the speaker circuit by the separate dc. power source.

The foregoing and other objects and advantages of the invention will be apparent from the following description, taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. la and lb are a schematic drawing of a signal generator module comprising a portion of a combination system in accordance with the present invention; and

FIG. 2a and 2b are a schematic drawing of an amplifier module for use in conjunction with the signal generator module, it being understood that a large number of amplifier modules of the type shown may be used in conjunction with a single signal generator module of the type shown.

Now, in order to acquaint those skilled in the art with the manner of making and using our invention, we shall describe, in conjunction with the accompanying drawings, a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, there is shown in FIG. I a plurality of terminals including terminals and 12 connected with a fire alarm relay l4, terminals 16 and 18 connected with a first general alarm relay 20, and terminals 22 and 24 connected with a second general alarm relay 26. When a fire alarm is initiated, a circuit is completed between the terminals 10 and 12 causing energization of the fire alarm relay 14. The fire alarm relay 14 may be energized by manually pulling a fire alarm box or by automatic sensing devices such as automatic smoke detectors, etc. In a similar manner, initiation of a first general alarm causes energization of the relay 20, and initiation of a second general alarm causes energization of the relay 26. There is further shown a voice communication relay 28 which as explained later herein is energized upon manual actuation of a microphone switch which permits voice transmission over the combination system described herein. It should therefore be understood in connection with the following description of the combination system of the present invention that initiation of a fire alarm energizes relay l4, initiation of a first general alarm energizes relay 20, initiation of a second general alarm energizes relay 26 and manual actuation of a microphone switch associated with a voice communication module energizes relay 28.

FIG. 1 further shows a pair offire tone signal generators 30 and 32, a first general tone signal generator 34 and a second general tone signal generator 36. A source of 24 volts dc power is indicated generally at 38 and is connected over lines 40 and 42 to a low voltage regulator indicated generally at 44. The low voltage regulator 44 produces a voltage of 12 volts on a line 46, 12 volts on a line 48, and 6 volts on a line 50. The 12 volt dc. power on line 46 is conducted over lines 46, 52 and 54 to a time delay unit indicated generally at 56. The line 54 includes a normally closed relay contact 280, and it will thus be understood that 12 volts dc. power is conducted to the time delay device 56 except upon activation of the voice communication module which energizes relay 28 and opens the relay contact 28a.

The purpose of the time delay device 56 is to provide a short delay in transmission of power from the 12 volt line 54 to the various tone generators 30, 32, 34 and 36. As will become more apparent from the following description, the fire tone generators produce continu ous signals which are utilized for the purpose of supervising the amplifier portion of the system, and under normal conditions the amplifiers are disconnected from the speaker lines. However, manual operation of a microphone switch for purposes of voice communication disconnects the fire tone signal generators from the amplifiers and from the power supply and causes the amplifiers to be connected to the speaker circuits. Accordingly. the time delay device 56 serves the purpose of delaying the power supply to the fire tone signal generators after use of the voice communication system, the delay serving to assure that the amplifiers have again been disconnected from the speaker lines before power is restored to the fire tone generators. In other words, the purpose of the time delay device 56 is to prevent sounding of a false fire alarm as might otherwise be caused subsequent to operation of the voice communication system.

The power output from the time delay device 56 is conducted over a power line 58. It will be seen that under normal conditions in the absence of any alarm signals the l2 volt dc. power on line 58 is conducted over lines 58, 60., 62. 64. 68, 70 and 72 to the input of the fire tone signal generator 30. The line 60 includes a relay contact 14a and the line 66 includes relay contacts 20a and 260, but each of the foregoing relay contacts is normally closed and thus 12 volt dc power is conducted to fire tone signal generator 30 under normal conditions in the absence of any alarm signals. Moreover, the above-mentioned line 70 connects with lines 74 and 76 leading to the input of the second fire tone signal generator 32. It will thus be understood that whenever power is supplied to the first fire tone signal generator 30 the interconnection provided by the lines 74 and 76 will supply power simultaneously to the second fire tone signal generator 32. It will further be understood that fire tone signal generators 30 and 32 are continuously supplied with power under normal conditions in the absence of any alarm signal. and in accordance with the present invention the continuous output from the fire tone signal generators is utilized to supervise the amplifier portion of the combination system.

The power supply line 60 connects with lines 78 and 80 leading to the input of the first general tone signal generator 34 for supplying 12 volts dc power to the latter. The line 78 includes a normally closed relay contact 26!) and the line 80 includes a normally open relay contact 20b. Thus, upon initiation of a first general alarm the relay 20 is energized thereby closing the relay contact 20b so as to supply power from the time delay unit 56 to the signal generator 34. In a similar manner, the line 78 connects with a line 82 leading to the input of the second general tone signal generator 36, and the line 82 includes a normally open relay contact 26c. Accordingly, when the second general alarm is initiated the relay 26 is energized thereby closing the relay Contact 26(- so as to supply power to the signal generator 36.

When a fire alarm is initiated. the relay 14 is ener gized thereby opening the relay contact 14a in the power supply line 60. When the relay contact 14a is open it is not possible to transmit power to either of the general tone signal generators 34 or 36 and thus fire tone signals take priority over the two general tone signals. A line 84 interconnects the power supply line 58 with the line 68 which leads to the inputs of the two fire tone signal generators 30 and 32. The line 84 includes a normally open relay contact 14b which is closed upon initiation of a fire alarm due to energization of the relay 14 thereby supplying 12 volts d.c. power to the fire tone signal generators 30 and 32 while disconnecting the power supply lines to the general tone signal generators 34 and 36. It will be borne in mind however that actuation of a microphone switch associated with the voice communication module energizes relay 28, in a manner to be explained hereinafter, with the result that the relay contact 28a in the power supply line 54 is opened thereby disconnecting the power supply from the time delay unit 56 so as to cut off power to all of the signal generators 30, 32, 34 and 36. Accordingly. in the combination system described herein, the voice communication module takes priority over the fire alarm and general alarm components of the system.

The output signals from the fire tone module 30 are conducted to the input of a first pre-amplifier 86 over a circuit comprising lines 88, 90, 92 and 94. The first general tone module 34 is connected to line 90 through an output line 96, and the second general tone moduie 36 is connected to the same output circuit through a line 98. The line 92 of the foregoing circuit includes a normally closed relay contact 281), and it will thus be noted that upon use of the voice communication micro phone the energization of the relay 28 will open the relay contact 28b thereby disconnecting the three tone modules 30, 34 and 36 from the pre-amplifier 86. The output signals from the second fire tone module 32 are connected to the input of a second pre-amplifier 100 over a circuit comprising lines 102 and 104. The line 102 includes a normally closed relay contact 2&- and thus upon use of the voice communication microphone the energization of the relay 28 will open the contact 280 and disconnect the fire tone module 32 from the second pre-amplifier 100.

As noted hereinabove, the voice communication module of the combination system described herein includes a microphone having a manually operable buttom switch or the like which is actuated in order to rendcr the voice communication module operative and disconnect the fire alarm and general alarm components of the system. The circuitry relating to actuation of the voice communication module is indicated generally at 106 and includes the relay 28, a pair of transistors 108 and 110, a power line 112 connected to the 24 volts dc power source 38, and a line 114 representing the negative side or ground of the circuit referred to herein as common.

A line 116 leading from a mike key terminal 118 to a point 120 in the circuit 106 is normally open, and under such conditions there will be a voltage at the point 120 of approximately 89 volts which is applied to the base of the transistor 110 to maintain the latter on whereby the transistor 108 will normally be maintained off. Consequently, the relay 28 will normally be deenergized. However, when the mike key or microphone switch is actuated the terminal 118 is shorted to one of the common" terminals such as shown at 122 and 124 thereby removing the voltage from the base of transistor 110 causing the latter to go off and causing the transistor 108 to go on and conduct. When the transistor 108 conducts a circuit is completed through the relay 28 and transistor 108 from the 24 volts dc. power line 112 to the common line 114 thereby energizing the relay 28.

A pair of terminals 126 and 128 and associated lines 130 and 132 transmit voice signals to an audio preamplifier 134. and the output from the pre-amplifler 134 is conducted to the pre-amplifier 86 through the circuit comprising lines 136, 138 and 94. The line 138 includes a normally open relay contact 28d which is closed when the relay 28 is energized upon actuation of the mike key. The output from the audio prc amplifier is also conducted to the second pre-amplifier 100 through the circuit comprising lines 136, 140 and 104, the normally open relay contact 280 in the line 140 being closed upon energization of the relay 28. It will further be noted that when the audio pre-amplifier 134 is connected to the two pre-amplifiers 86 and 100 upon energization of relay 28, the relay contact 28b in the line 92 and the relay contact 28 in the line 102 are opened thereby disconnecting the various tone modules 30, 32, 34 and 36 from the corresponding preamplifiers 86 and 100. The output signals from the preamplifier 86 are conducted along line 142 to terminal 144, and the output signals from pre-amplifier are conducted along line 146 to terminal 148.

In accordance with the present invention, there is provided a control line 150 which transmits a predetermined voltage depending upon the condition of the system. Thus, under normal conditions in the absence of an alarm, the line 50 which extends from the voltage regulator 44 and which carries 6 volts d.c. is connected to the control line 150 through a circuit comprising lines 152, 154, 156 and 158, whereby the control line will conduct 6 volts dc. to a control terminal 160. When a fire alarm is initiated, the line 48 which extends from the voltage regulator and carries 12 volts do is connected to the control line 150 through a circuit comprising lines 152, 154, 156 and 158. The line 48 includes a normally open relay contact 146 which will be closed during a fire alarm condition due to energization of the relay 14.

When the voice communication module is activated, the 24 volts dc. power source 38 will be connected to the control line 150 through a circuit comprising lines 166, 168, 170, 172, 156 and 158. The line 172 includes a normally open relay contact 28f which will be closed during activation of the voice communication module due to energization of the relay 28. When the first gen eral alarm is activated causing energization of relay 20, the 24 volts dc. power source 38 will be connected to the control line 150 through a circuit comprising lines 166, 168, 170, 174, 176, 178 and 158. The line 178 includes a normally open relay contact 200 which will be closed upon energization of the relay 20. It will further be noted that the line 174 includes a normally closed relay contact 14d which opens during a fire alarm condition thereby preventing 24 volts d.c. form being conducted to the control line 150. When the second general alarm is activated causing energization of relay 26, the 24 volts dc. power source 38 will be connected to the control line 150 through a circuit comprising lines 166, 168, 170, 174, 180, 154, 156 andd 158. The line 180 includes a normally open relay contact 26d which will be closed upon energization of relay 26. It will now be understood that under normal conditions in the absence of any alarm the control line 150 will conduct 6 volts d.c.; during a fire alarm condition the control line will conduct 12 volts d.c.; and when either of the two general alarms or the voice communication module is activated, the control line will carry 24 volts do However, a general alarm will not produce 24 volts d.c. on the control line ifa fire alarm is also initiated due to the relay contact 14d which gives priority to the fire alarm, whereas activation of the voice communication module will also produce 24 volts do on the control line. The purpose of the foregoing control line 150 will be explained more fully hereinafter.

Reference is now made to a trouble circuit for providing a trouble signal in the event a problem is detected in the operation of the system. A pair of terminals 182 and 184 and associated lines 186 and 188 comprise a trouble loop. As will be described hereinafter, the terminals 182 and 184 are normally shorted together to provide a closed trouble loop circuit, and when a problem is detected the foregoing terminals are disconnected thereby opening the trouble loop. The trouble loop circuitry includes a trouble relay 190 and a transistor 192. The line 186 connects with the 24 volts dc power line 112, and thus as long as the trou ble loop is closed a voltage will be applied by line 188 to the base of transistor 192 so that the latter will be on and will conduct.

It will further be seen that while the transistor 192 is conducting, a circuit is completed between the power supply line 112 and the common line 114 which circuit includes the relay 190 and transistor 192, whereby the relay 190 is normally maintained energized. A terminal 194 representing 24 volts d.c. input is connected to the common line 114 through a circuit including a relay contact 190a and a trouble light 196. Since the relay 190 is maintained energized in the absence of trouble, the relay contact 190a will be maintained open and the trouble light 196 will not be activated. However, whenever the terminals 182 and 184 are disconnected due to detection of a problem with the system, as will be explained later herein, the relay 190 will be deenergized, the relay contact 190a will be closed, and the trouble light 196 will be activated. It will of course be understood that various types of trouble indicators including audible signals may be provided in addition to the trouble light 196 which is described by way of example only. Thus, there are illustrated additional trouble indication circuits 193 and 195 associated with terminals 197, 199 and 201. The foregoing circuits includes relay contacts 1901) and 1906. If the above-described trouble loop is opened deenergizing the normally-energized relay 190, the contact 1901: will be opened and the relay 190:- will be closed thereby affording means for effecting such additional trouble indications as may be desired.

Reference is now made to FIG. 2 which illustrates the amplifier and speaker circuits for the combination system of the present invention. The output signal from the pre-amplifier 86 is conducted from terminal 144 over a line 198 to a first power amplifier 200, and the output signal from the pre-amplifier 100 is conducted from terminal .148 over a line 202 to a second power amplifier 204. A line 205 supplies 24 volts d.cv to the amplifier 200, and power is supplied over line 207 to the amplifier 204. A supervision and switching circuit 209 associated with the control line 150 controls the switching between the power amplifiers and the speaker network. It will be borne in mind that the control line 150 carries 6 volts do under normal conditions in the absence of an alarm signal. The control line 150 connects with three parallel lines 206, 208 and 210, and the latter three lines include respective diodes 212, 214 and 216 so as to transmit a signal from the control line 150 only in the event the voltage on the line 150 is above a predetermined value. In the particular embodiment being described, the diode 212 will conduct a signal exceeding 3.3 volts, the diode 214 will conduct a signal exceeding 16 volts and the diode 216 will conduct a signal exceeding 8.2 volts. Accordingly, when the control line 150 carries 6 volts d.c., as under normal conditions, a signal will be conducted past the diode 212 but will be blocked by the diodes 214 and 216.

The circuit associated with the line 206 and diode 212 includes a pair of transistors 218 and 220, the transistor 218 being normally on so as to conduct. and the transistor 220 being normally off, providing the normal 6 volt signal is being conducted past the diode 212 to the base of the transistor 218. The foregoing components control the state of a transistor 222 associated with the trouble loop described hereinabove. Thus. the

base of the transistor 222 is connected through lines 224 and 226 to a 24 volts dc. power supply line 228 whereby the transistor 222 is normally on so as to conduct. A circuit is provided between the power supply line 228 and a common line 230 which comprises line 232, transistor 222, trouble relay 234 and line 236. Accordingly, as long as the transistor 222 is conducting, a closed circuit is provided between power line 228 and the common 230 thereby maintaining the trouble relay 234 energized. FIG. 2 shows the previously described terminals 182 and 184 which are normally shorted together to form a closed trouble loop. Thus, the terminals 182 and 184 are connected by a line 233 which includes a relay contact 234a. The normally energized trouble relay 234 maintains the contact 2340 closed. However, whenever a malfunction causes deenergization of the trouble relay 234, the contact 234a is opened thus opening the trouble loop shown in FIG. 1 and producing the previously described signals such as activation of trouble light 196. It should be understood that the trouble indication circuit illustrated in conjunction with the signal generator module of FIG. 1 is intended to provide a trouble signal at a central control station where the signal generator module is located. It should further be understood that a plurality of remotely located amplifier modules may be associated with the trouble loop or trouble actuation circuit at the central control station so as to provide a trouble signal if a malfunction occurs at any of the remote amplifier modules. An additional trouble indication may be provided in conjunction with each of the remote amplifier modules so as to indicate trouble with that particular module. Thus, there is shown a line 235 connected between the power supply line 228 and the common line 230 and including a relay contact 23412 and a trouble light 237. As long as the trouble relay 234 remains energized the contact 234b will be open, but when a malfunction causes deenergization of relay 234 the contact 2341: will close activating trouble light 237 thereby providing a trouble signal associated with a corresponding remote amplifier module.

One condition which will produce a trouble indication is loss of the normal 6 volts d.c. signal on the control line 150. If the 6 volt signal is lost then the transistor 218 goes off causing the transistor 220 to turn on and conduct. When the transistor 220 conducts it completes a circuit between a common and the base of transistor 222, such circuit including common 238, transistor 220, and lines 240, 242 and 224. Consequently, the base of transistor 222 is connected to common turning the transistor off and causing trouble relay 234 to be deenergized thereby initiating a trouble sig nal. In this manner the control line and related circuitry is supervised to assure that the same is function ing properly.

Still referring to the circuits associated with the control line 150, when a fire alarm is initiated thereby energizing the fire alarm relay 14, the control line 150 carries 12 volts d.c. as previously described. Accordingly, upon initiation of a fire alarm, :1 l2 volts d.c. signal is conducted past the diode 216 over a line 244 and applied to the base of transistor 246. The transistor 246 and an associated transistor 248 are both normally off. However, when a l2 volts d.c. signal is conducted past diode 216 to the base of transistor 246 the latter is turned on and it turns on transistor 248 thereby causing the latter to conduct. The transistor 248 when caused to conduct completes a circuit to effect energization of a relay 250. The relay 250 is in a circuit comprising 24 volts dc. power supply line 228, line 252, relay 250, lines 254 and 256, transistor 248 and lines 258 and 260 which lead to common Thus, when a fire alarm is initiated, the control line 150 will carry a 12 volts d.c. signal causing transistor 248 to conduct and thereby effecting energization of relay 250.

The relay 250 in conjunction with a pair of detectors 262 and 264 controls the circuits which connect the amplifiers 200 and 204 with the speaker lines associated therewith. Thus, the detectors 262 and 264 will now be described, and reference is first made to the detector 262 which is associated with the first power amplifier 200. The output signal from the power amplifier 200 is conducted over lines 266 and 268 and, after conversion to a dc. signal by a rectifier 269, is applied to the base of a transistor 270 to maintain the latter on which in turn maintains an associated transistor 272 off so that the latter will not conduct. However, if the output signal from the amplifier 200 is lost, the transistor 270 will go off thereby turning the transistor 272 on causing the latter to conduct. The transistor 272 is in a circuit comprising line 274 which is connected to common, transistor 272, lines 276 and 278, relay 280, and line 282 which is connected to the 24 volts d.c. power supply line 228. It will thus be understood that when the detector 262 senses the absence of an output signal from power amplifier 200, the transistor 272 is caused to conduct thereby effecting energization of relay 280. A pair of resistors 27] and 273 and a capacitor 275 are provided in the detector circuit between the rectifier 269 and the transistor 270 to afford a predetermined time delay before transistor 270 will turn off. Such a time delay is introduced so that the fire tone signal need not be continuous, and an interruption in the signal for less than a brief predetermined time interval will not effect energization of the relay 280.

The circuit between the power amplifier 200 and the speaker lines includes various contacts controlled by the above-described relays 250 and 280. Specifically, the amplifier 200 is connected through lines 266, 284, 286 and 288 to a first speaker line 290. A line 292 connects the line 288 with a second speaker line 294, and the two parallel speaker lines 290 and 294 are connected to a line 296 which connects with the previously described common line 230. The line 286 includes a normally open relay contact 250a, and the line 184 includes a normally closed relay contact 280a. In addition, lines 298 and 300 connect the output from the second amplifier 204 with the line 286 leading to the speaker circuits, and the line 300 includes a normally open relay contact 280h. It will thus be understood that under normal conditions in the absence ofan alarm signal the output from the amplifier 200 is connected with the detector 262 but is disconnected from the speaker circuits due to the normally open relay contact 250a, and the output from the second amplifier 204 is connected through lines 298 and 302 to the second detector 264 but is disconnected from the speaker lines due to the open contacts 250a and 280i).

Whenever an alarm signal is initiated, the control line 150 will conduct a signal, i.e., l2 volts d.c. for a fire alarm and 24 volts do for a general alarm or upon activation of the voice communication module, which effects energization of the relay 250, in which event the relay contact 2500 is closed and the first amplifier 200 is connected with the speaker circuits. The second amplifier 204 will remain disconnected from the speaker circuits during an alarm condition unless the detector 262 senses the absence of an output from the amplifier 200 in which event the relay 280 will be energized opening the contact 280a and closing the contact 28012. Accordingly, when the detector 262 senses the absence of an output from the first amplifier 200, the latter is disconnected from the speaker circuit and the second amplifier 204 is connected, providing an alarm condition has been initiated or the voice communication module has been activated so as to close the relay contact 250a.

In addition to switching from the first amplifier 200 to the second amplifier 204 when the first amplifier fails to produce an output, the detector 262 also initiates a trouble signal. When the detector 262 senses the absence of a signal from the amplifier 200 thereby causing transistor 272 to conduct as described above, a circuit is completed which includes common line 274, transistor 272 and lines 304, 306, 242 and 224 leading to the base of transistor 222. As previously described, when the base of transistor 222 is connected to common, the trouble relay 234 is deenergized and a trouble signal is initiated.

The detector 264 associated with the second amplifier 204 operates in a manner similar to the first detector 262 with respect to initiation of a trouble signal, but it does not effect a switching function. The output signal from the second amplifier 204 is conducted over lines 298 and 302 to a rectifier 308 which converts the output to a dc. signal which is applied to the base of a transistor 310 whereby the latter is normally maintained on and an associated transistor 312 is normally maintained off. If the detector 264 senses the absence of an output signal from the amplifier 204 then the transistor 310 will turn off causing the transistor 312 to turn on and conduct. When the transistor 312 conducts it completes a circuit comprising common line 314, transistor 312 and lines 316, 306, 242 and 224 leading to the base of transistor 222, and as previously described a trouble signal is initiated when the base of transistor 222 is connected to common.

It will be noted that the line 198 leading to the input of the amplifier 200 includes a resistance 318 and a by pass line having a normally open relay contact 250b. Under normal conditions in the absence of an alarm signal or activation of the voice communication module the contact 2501) will be open and the amplifier 200 will operate on reduced power. However, when an alarm condition is initiated or the voice communication module is activated, the relay 250 is energized as previously described thereby closing the by-pass contact 250!) so that full power is transmitted to the amplifier 200. In a somewhat similar manner, the line 202 leading to the input of the second amplifier 204 includes a resistance 320 and a by-pass line having a pair of normally open contacts 250C and 280a. The amplifier 204 will normally operate on reduced power. However, full power will be supplied to amplifier 204 if two conditions are met, namely, if an alarm is initiated or the voice communication module is activated so as to energize relay 250 and effect closing of contact 250a, and if detector 262 senses the absence of an output from the first amplifier 200 so as to energize relay 280 and effect closing of contact 2800 A further function of the control line 150 which will now be described concerns disabling of the detectors 262 and 264 under certain conditions. In accordance with the combination system of the present invention, the detectors 262 and 264 will function under normal conditions in the absence of an alarm signal, and they will also function during a fire alarm condition. However, the present system is designed to disable the detectors when a general alarm signal is initiated or when the voice communication module is activated. In this manner, the system will accommodate the use of various types of general alarm signals which are not necessarily continuous. Moreover, it is not believed practical to utilize the detectors when the voice communication module is activated since voice communication will necessarily produce non-continuous signals.

The detector 264 includes a pair of resistors 322 and 324 and a capacitor 326 which afford a time delay before the transistor 310 is turned off, and the detector 262 affords a similar time delay as previously described. However, such a time delay is not intended to accommodate significant interruptions of signals as might be produced by certain types of general alarm signals or by voice communication. Accordingly, whenever a general alarm signal is initiated, or the voice communication module is activated, as previously described the control line 150 will carry a 24 volts d.c. signal, and such signal will be conducted past the diode 214 so as to produce signals on the parallel lines 328 and 330. The line 328 transmits the foregoing signal to the detector 262 whereby the signal is applied to the base of transistor 270 to maintain the latter on without regard to whether an output signal is received from the amplifier 200. in a similar manner, the line 330 transmits a signal to the detector 264 where the signal is ap plied to the base of transistor 310 to maintain the latter on without regard to whether an output signal is received from the amplifier 204.

In the foregoing manner, the two detectors 262 and 264 are disabled whenever the control line 150 carries a signal of 24 volts d.c. It will of course be noted that under normal conditions or during a fire alarm condition the voltage on the control line is less than l6 volts, i.e., 6 volts or [2 volts respectively, and thus such lower voltage signals are blocked by the diode 214. However, while the detectors 262 and 264 are disabled under certain conditions as described above, the present system is designed so that if the detector 262 senses a loss of output from the amplifier 200 and thereby effects energization of the relay 280 so as to disconnect the amplifier 200 from the speaker circuits and connect the alternate amplifier 204 to such circuits, provision is made to maintain the relay 280 energized even though the detectors are subsequently disabled.

In order to accomplish the foregoing, a circuit is provided comprising 24 volts dc power supply line 282, relay 280, lines 278, 332, 256, transistor 248 and lines 258 and 260 which lead to common. The line 332 includes a normally open relay contact 280d which is closed when relay 280 is energized. Moreover, as previously described the transistor 248 will conduct whenever there is an alarm condition or the public address system is activated. Therefore, whenever the detector 262 senses loss of an output from amplifier 200 and switches in alternate amplifier 204, the subsequent activation of the voice communication module thereby disabling the detectors will not disconnect the alternate amplifier 204 as the closing of the relay contact 280d will maintain the relay 280 energized under such conditions. it will be recalled that fire alarm signals and voice communication signals are conducted to both amplifi ers 200 and 204, while in the system described herein general alarm signals are conducted only to the amplifier 200.

In accordance with the combination system of the present invention as described herein, the amplifier circuit is supervised by continuous fire tone signals from the fire tone modules 30 and 32, and under normal conditions in the absence of an alarm the amplifier circuit is disconnected from the speaker lines. The speaker circuit is supervised by a separate d.c. power source, and in the embodiment described each of the two speaker lines is independently supervised. However, during an alarm condition the speaker lines 290 and 294 are not supervised but are connected in parallel with the output from the power amplifier 200. Re ferring first to the speaker line 290, a dc. supervisory circuit is indicated generally at 334 and comprises line 228 which is connected to the 24 volts dc power source, and lines 336, 338, 340 and 288, the latter being connected with the speaker line 290 which as previously described is connected with a speaker common line 296. The line 336 includes a resistor 342, and the line 340 includes a normally closed relay contact 250d. The speaker line 290 further includes an end of line resistor 344. In addition, a plurality of horn assemblies are connected in parallel in the speaker circuit between the speaker line 290 and the common line 296, and one such horn assembly is shown by way of example at 346. A capacitor such as shown at 348 is associated with each horn assembly, and a stepdown transformer 350 is provided for reducing the voltage to approximately 4 volts.

The voltage at point 352 in the dc supervisory cir cuit 334 will be approximately 7 voltsv The circuit fur ther includes a pair of diodes 354 and 356, the diode 354 being designed to block voltage signals which do not exceed 9.1 volts, and the diode 356 being designed to block voltage signals which do not exceed 3.3 volts. Thus, under normal conditions a voltage signal will be conducted on line 358 past diode 356 and thus transmitted by line 360 to the base of a transistor 362 thereby maintaining the latter normally on which in turn maintains the associated transistor 364 normally off so that the latter will not conduct. However, if a short occurs in speaker line 290, the voltage on line 358 will ball below 3.3 volts and thus will be blocked by the diode 356 with the result that the transistor 362 will go off causing the associated transistor 364 to go on and conduct. The transistor 364 is in a circuit including line 366 which is connected to common, transistor 364, and lines 368, 370, 372 and line 224 leading to the base of transistor 222. Accordingly, when the transistor 364 in the dc supervisory circuit 334 is caused to conduct due to a short in the speaker line 290, the transistor 222 will go off and deenergize trou ble relay 234 thereby producing a trouble signal in the manner previously described, Moreover. in the event an open circuit develops in the speaker line 290, the removal of the end of line resistor 344 will cause the Volt age at point 352 to exceed 9. l volts so that a signal will be conducted over lines 374, 376 and 378 to the base of a transistor 380 so that the latter which is normally off will be turned on and caused to conductv The transistor 380 is in a circuit including line 366 which is connected to common, lines 382 and 384, transistor 380, line 386 and line 370 which leads to the base of the transistor 222 in the trouble circuit. Thus, if the speaker line 290 develops an open circuit, the transistor 380 is caused to conduct thereby connecting common to the base of the transistor 222 which as previously described produces a trouble signal.

The second speaker line 294 includes a plurality of horn assemblies and related components which are the same as those connected with the first speaker line 290 and thus are identified by corresponding primed reference numerals. Moreover, a second d.c. supervisory circuit is indicated generally at 334', and since the latter functions in the same manner as the supervisory circuit 334 a detailed description will not be provided herein. It will be noted however that the line 292 includes a normally open relay contact 250a. Accordingly, the two speaker lines are independently supervised, but when an alarm signal is initiated or when the voice communication module is activated, the energization of relay 250 as previously described will close contact 2500 thereby connecting the two speaker lines 290 and 294 in parallel with the amplifier output line 288. In addition, a line 386 is connected with the d.c. supervisory circuit at line 338 so as to connect the latter with common line 230. Line 386 includes a normally open relay contact 250f and also a IK resistor 388 having the same resistance as the end-of-line resistor 344 in the speaker line 290. During an alarm condition when the supervisory circuit 334 is disconnected from the speaker line 290 due to the opening of contact 250d, the contact 250] will be closed so as to connect the [K resistor 388 in the circuit. The resistance 388 will thus function as a dummy load to replace end-ofline resistor 344 and thereby prevent initiation of false trouble signals during an alarm condition when the supervisory circuit 334 is disconnected from the speaker line 290.

It is important to note that by utilizing d.c. supervision of the speaker line 290 and connecting each horn assembly 346 in conjunction with a capacitor 348, the horn assemblies are isolated from the d.c. supervisory signal during supervision of the speaker line but are not isolated from the ac output signal received from the amplifier circuit during an alarm condition or when the voice communication module is activated.

In the use of a combination system of the type described herein, it is possible to power several hundred amplifiers from a single tone generator module. In the particular system described herein, the output from each of the alternate power amplifiers 200 and 204 is 76 watts, and since each speaker or horn assembly 346 requires 2 watts, it is feasible to utilize 36 horn assemblies in conjunction with the amplifier module comprising alternate amplifiers 200 and 204. In the present embodiment, two speaker lines are shown, and thus a total of 36 speakers can be accommodated and divided equally or in any other desired proportion between the two speaker lines 290 and 294.

In the preferred embodiment as described herein, the alarm signals comprise a fire alarm signal and a plurality of general alarm signals, in combination with voice communication, and the system is designed so that voice Signals take priority over alarm signals, and the primary alarm signal, i.e., the fire alarm signal, takes priority over the various general alarm signals. While it is believed that in most applications of the foregoing system the primary alarm signal will comprise a fire alarm, it will be understood that the present invention is not limited to this particular application and an alarm signal other than a fire alarm may comprise the primary alarm signal.

It will further be understood that in accordance with one of the features of the present invention, a continuously operable alarm signal is utilized to supervise the amplifier circuit. In accordance with a preferred embodiment of the invention, the primary alarm signal, e.g., the firetone signal, is utilized for the foregoing purpose. Such an arrangement eliminates the need for ad ditional means to supervise the firetone signal generator as would otherwise be necessary under various existing code requirements. However, if desired, one of the other alarm signals, such as a general alarm signal, may be utilized to supervise the amplifier circuit, since it will be understood that in either case there is achieved the important advantage that the speaker circuits are disconnected from the amplifier circuit under normal conditions thereby completely eliminating any undesirable noise from the speakers during normal supervision of the system.

We claim:

I. An alarm and emergency voice communication system comprising, in combination, alarm signal generating means continuously operable under normal conditions, voice communication means, amplifier circuit means, speaker circuit means, separate d.c. supervisory circuit means including a d.c. supervisory source, means connecting said voice communication means with said amplifier circuit means when said voice communication means is activated, switch means normally maintaining said alarm signal generating means connected with said amplifier circuit means, normally maintaining said amplifier circuit means disconnected from said speaker circuit means and normally main taining said d.c. supervisory power source connected to said speaker circuit means whereby an alarm signal is utilized to supervise said amplifier circuit means and a separate d.c. signal is utilized to supervise said speaker circuit means, and control means responsive to an alarm for activation of said switch means.

2. An alarm and emergency voice communication system as defined in claim 1 including control means responsive to initiation of an alarm or activation of said voice communication means for causing said switch means to connect said amplifier circuit means with said speaker circuit means and disconnect said d.c. supervisory power source from said speaker circuit means.

3. An alarm and emergency voice communication system comprising, in combination, alarm signal generating means continuously operable under normal conditions, voice communication means, amplifier circuit means, speaker circuit means, separate d.c. supervisory circuit means including a d.c. supervisory power source, switch means normally maintaining said alarm signal generating means connected with said amplifier circuit means, normally maintaining said amplifier circuit means disconnected from said speaker circuit means and normally maintaining said d.c. supervisory power source connected to said speaker circuit means whereby an alarm signal is utilized to supervise said amplifier circuit means and a separate d.c. signal is utilized to supervise said speaker circuit means, first control means responsive to initiation of an alarm or activation of said voice communication means for causing said switch means to connect said amplifier circuit means with said speaker circuit means and disconnect said d.c. supervisory power source from said speaker means, and second control means responsive to activation of said voice communication means for disabling said alarm signal generating means and connecting said voice communication means to said amplifier circuit means.

4. An alarm and emergency voice communication system as defined in claim 3 wherein said speaker circuit means includes a plurality of speakers connected in parallel, and capacitor means connected with said speakers for isolating said speakers from said separate d.c. supervisory signal while permitting normal operation of said speakers when said amplifier circuit means is connected with said speaker circuit means.

5. An alarm and emergency voice communication system as defined in clain 3 including detector means connected with the output of said amplifier circuit means, said detector means being responsive to a loss of output signal from said amplifier circuit means so as to initiate a trouble indication.

6. An alarm and emergency voice communication system as defined in claim 5 wherein said amplifier circuit means includes first and second alternate amplifiers and said detector means operates in response to loss of output signal from said first amplifier to disconnect the latter and connect second amplifier in said amplifier circuit means.

7. An alarm and emergency voice communication system as defined in claim 5 including control means responsive to activation of said voice communication means for disabling said detector means.

8. An alarm and emergency voice communication system as defined in claim 3 wherein said alarm signal generating means includes first and second alarm signal generators and said amplifier circuit means includes first and second alternate amplifiers, said first alarm signal generator normally being operatively connected with said first amplifier and said second alarm signal generator normally being operatively connected with said second amplifier, and control means responsive to activation of said voice communication means for disabling said first and second alarm signal generator and operatively connecting said voice communication means both to said first and second amplifiers.

9. An alarm and emergency voice communication system as defined in claim 3 wherein said speaker circuit means includes a plurality of speaker lines, each speaker line supplying a plurality of speakers connected in parallel, a plurality of separate d.c. supervisory circuits including a dc. power source connected respectively with each of said speaker lines for independent supervision thereof, and control means responsive to initiation of an alarm or activation of said voice communication means for disconnecting each of said speaker lines from its corresponding d.c. supervisory circuit and for connecting said plurality of speaker lines in parallel with said amplifier circuit means.

10. An alarm and emergency voice communication system as defined in claim 3 wherein said d.c. supervisory circuit means includes first voltage sensing means responsive to a voltage in excess of a first predetermined value for sensing an open speaker circuit and ini tiating a trouble indication, and second voltage sensing means responsive to a voltage below a second predeter mined value for sensing a shorted speaker circuit and initiating a trouble indication. said d.c. supervisory circuit normally producing a voltage at said first and second sensing means having a magnitude intermediate said first and second predetermined values in the absence of an open or shorted speaker circuit.

11. An alarm and emergency voice communication system as defined in claim 3 including primary tone signal generating means and at least one general tone signal generating means, power supply means for supply ing power to said primary tone signal generating means and said general tone signal generating means, said power supply means normally being connected with said primary tone signal generating means and disconnected from said general tone signal generating means, first control means responsive to initiation of a general alarm for disconnecting said power supply means from said primary tone signal generating means and connecting said power supply means to said general tone signal generating means, and second control means connected in overriding relation to said first control means and responsive to initiation of a primary alarm for dis connecting said power supply means from said general tone signal generating means and connecting said power supply means to said primary tone signal generating means.

12. An alarm and emergency voice communication system comprising, in combination, alarm signal generating means continuously operable under normal con ditions, voice communication means, amplifier circuit means, speaker circuit means, separate d.c. supervisory circuit means including a dc supervisory power source, switch means normally maintaining said alarm signal generating means connected with said amplifier circuit means, normally maintaining said amplifier circuit means disconnected from said speaker circuit means and normally maintaining said d.c. supervisory power source connected to said speaker circuit means whereby an alarm signal is utilized to supervise said amplifier circuit means and a separate d.c. signal is utilized to supervise said speaker circuit means, first control means responsive to initiation of an alarm or activation of said voice communication means for causing said switch means to connect said amplifier circuit means with said speaker circuit means and disconnect said d.c. supervisory power source from said speaker circuit means, second control means responsive to activation of said voice communication means for disabling said alami signal generating means and connecting said voice communication means to said amplifier circuit means, detector means connected with the output of said amplifier circuit means, said amplifier circuit means including first and second alternate amplifiers and said detector means operating in response to loss of output signal from said first amplifier to disconnect the latter and connect said second amplifier in said am plifier circuit means and also to initiate a trouble indication, and third control means responsive to activation of said voice communication means for disabling said detector means.

13. An alarm and emergency voice communication system as defined in claim 12 wherein said speaker cir cuit means includes a plurality of speakers connected in parallel, and capacitor means connected with said speakers for isolating said speakers from said d.c. supervisory signal while permitting normal operation of said speakers when said amplifier circuit means is connected with said speaker circuit means.

14. An alarm and emergency voice communication system as defined in claim 12 wherein said alarm signal generating means includes first and second alarm signal generators, said first alarm signal generator normally being operatively connected with said first amplifier and said second alarm signal generator normally being operatively connected with said second amplifier, and wherein said second control means operates in response to activation of said voice communication means to disable said first and second alarm signal generators and operatively connect said voice communication means both to said first and second amplifiers.

15. An alarm and emergency voice communication system comprising, in combination, alarm signal gener ating means, voice communication means, amplifier circuit means, speaker circuit means, said alarm signal generating means normally being connected with said amplifier circuit means, said speaker circuit means normally being disconnected from said amplifier circuit means, and said voice communication means when ac tivated being connected with said amplifier circuit means, first control means responsive to initiation of an alarm for operatively connecting said amplifier circuit means and speaker circuit means thereby causing an alarm signal to be conducted to said speaker circuit, and second control means responsive to activation of said voice communication means and connected in overriding relation to said first control means for disabling said alarm signal generating means and operatively connecting said voice communication means with said amplifier circuit and speaker circuit thereby enabling voice signals to be conducted to said speaker circuit,

16. An alarm and emergency voice communication system as defined in claim 15 wherein said alarm signal generating means includes first and second alarm signal generators and said amplifier circuit means includes first and second alternate amplifiers, said first control means operatively connecting said first alarm signal generator with said first amplifier and said second alarm signal generator with said second amplifier, and said second control means operatively connecting said voice communication means with both said first and second amplifiers.

17. An alarm and emergency voice communication system as defined in claim 16 wherein said first amplifier is nonnally connected in said speaker circuit means and said second amplifier is disconnected, and detector means responsive to a loss of output signal from said first amplifier for disconnecting the latter and connecting said second amplifier in said amplifier circuit means, and third control means responsive to activation of said voice communication means for disabling said detector means.

18. In an alarm and emergency voice communication system of the type having alarm signal generating means, voice communication means, amplifier circuit means and speaker circuit means, an improved d.c. supervisory circuit for detecting both an open and a shorted speaker circuit comprising, in combination, a dc. supervisory circuit including a dc. power source connected with a speaker circuit to be supervised, first voltage sensing means which blocks voltage signals less than a first predetermined voltage while conducting higher voltage signals, second voltage sensing means which blocks voltage signals less than a second predetermined voltage while conducting higher voltage signals, circuit means interconnecting said first and second voltage sensing means, means in said supervisory circuit operable in the absence of an open or shorted circuit for producing at said circuit means a normal voltage intermediate said first and second predetermined voltage whereby said normal voltage is blocked by said first sensing means and conducted by said second sensing means, first trouble circuit means connected with said first voltage sensing means for producing a trouble signal in response to a voltage signal conducted past said first voltage sensing means in the event of an open speaker circuit, and second trouble circuit means connected with said second voltage sensing means for producing a trouble signal in response to blockage of a voltage signal by said second voltage sensing means when a short occurs in said speaker circult. 

1. An alarm and emergency voice communication system comprising, in combination, alarm signal generating means continuously operable under normal conditions, voice communication means, amplifier circuit means, speaker circuit means, separate d.c. supervisory circuit means including a d.c. supervisory source, means connecting said voice communication means with said amplifier circuit means when said voice communication means is activated, switch means normally maintaining said alarm signal generating means connected with said amplifier circuit means, normally maintaining said amplifier circuit means disconnected from said speaker circuit means and normally maintaining said d.c. supervisory power source connected to said speaker circuit means whereby an alarm signal is utilized to supervise said amplifier circuit means and a separate d.c. signal is utilized to supervise said speaker circuit means, and control means responsive to an alarm for activation of said switch means.
 2. An alarm and emergency voice communication system as defined in claim 1 including control means responsive to initiation of an alarm or activation of said voice communication means for causing said switch means to connect said amplifier circuit means with said speaker circuit means and disconnect said d.c. supervisory power source from said speaker circuit means.
 3. An alarm and emergency voice communication system comprising, in combination, alarm signal generating means continuously operable under normal conditions, voice communication means, amplifier circuit means, speaker circuit means, separate d.c. supervisory circuit means including a d.c. supervisory power source, switch means normally maintaining said alarm signal generating means connected with said amplifier circuit means, normally maintaining said amplifier circuit means disconnected from said speaker circuit means and normally maintaining said d.c. supervisory power source connected to said speaker circuit means whereby an alarm signal is utilized to supervise said amplifier circuit means and a separate d.c. signal is utilized to supervise said speaker circuit means, first control means responsive to initiation of an alarm or activation of said voice communication means for causing said switch means to connect said amplifier circuit means with said speaker circuit means and disconnect said d.c. supervisory power source from said speaker means, and second control means responsive to activation of said voice communication means for disabling said alarm signal generating means and connecting said voice communication means to said amplifier circuit means.
 4. An alarm and emergency voice communication system as defined in claim 3 wherein said speaker circuit means includes a plurality of speakers connected in parallel, and capacitor means connected with said speakers for isolating said speakers from said separate d.c. supervisory signal while permitting normal operation of said speakers when said amplifier circuit means is connected with said speaker circuit means.
 5. An alarm and emergency voice communication system as defined in clain 3 including detector means connected with the output of said amplifier circuit means, said detector meaNs being responsive to a loss of output signal from said amplifier circuit means so as to initiate a trouble indication.
 6. An alarm and emergency voice communication system as defined in claim 5 wherein said amplifier circuit means includes first and second alternate amplifiers and said detector means operates in response to loss of output signal from said first amplifier to disconnect the latter and connect second amplifier in said amplifier circuit means.
 7. An alarm and emergency voice communication system as defined in claim 5 including control means responsive to activation of said voice communication means for disabling said detector means.
 8. An alarm and emergency voice communication system as defined in claim 3 wherein said alarm signal generating means includes first and second alarm signal generators and said amplifier circuit means includes first and second alternate amplifiers, said first alarm signal generator normally being operatively connected with said first amplifier and said second alarm signal generator normally being operatively connected with said second amplifier, and control means responsive to activation of said voice communication means for disabling said first and second alarm signal generator and operatively connecting said voice communication means both to said first and second amplifiers.
 9. An alarm and emergency voice communication system as defined in claim 3 wherein said speaker circuit means includes a plurality of speaker lines, each speaker line supplying a plurality of speakers connected in parallel, a plurality of separate d.c. supervisory circuits including a d.c. power source connected respectively with each of said speaker lines for independent supervision thereof, and control means responsive to initiation of an alarm or activation of said voice communication means for disconnecting each of said speaker lines from its corresponding d.c. supervisory circuit and for connecting said plurality of speaker lines in parallel with said amplifier circuit means.
 10. An alarm and emergency voice communication system as defined in claim 3 wherein said d.c. supervisory circuit means includes first voltage sensing means responsive to a voltage in excess of a first predetermined value for sensing an open speaker circuit and initiating a trouble indication, and second voltage sensing means responsive to a voltage below a second predetermined value for sensing a shorted speaker circuit and initiating a trouble indication, said d.c. supervisory circuit normally producing a voltage at said first and second sensing means having a magnitude intermediate said first and second predetermined values in the absence of an open or shorted speaker circuit.
 11. An alarm and emergency voice communication system as defined in claim 3 including primary tone signal generating means and at least one general tone signal generating means, power supply means for supplying power to said primary tone signal generating means and said general tone signal generating means, said power supply means normally being connected with said primary tone signal generating means and disconnected from said general tone signal generating means, first control means responsive to initiation of a general alarm for disconnecting said power supply means from said primary tone signal generating means and connecting said power supply means to said general tone signal generating means, and second control means connected in overriding relation to said first control means and responsive to initiation of a primary alarm for disconnecting said power supply means from said general tone signal generating means and connecting said power supply means to said primary tone signal generating means.
 12. An alarm and emergency voice communication system comprising, in combination, alarm signal generating means continuously operable under normal conditions, voice communication means, amplifier circuit means, speaker circuit means, separate d.c. supervisory circuit means including a d.c. superviSory power source, switch means normally maintaining said alarm signal generating means connected with said amplifier circuit means, normally maintaining said amplifier circuit means disconnected from said speaker circuit means and normally maintaining said d.c. supervisory power source connected to said speaker circuit means whereby an alarm signal is utilized to supervise said amplifier circuit means and a separate d.c. signal is utilized to supervise said speaker circuit means, first control means responsive to initiation of an alarm or activation of said voice communication means for causing said switch means to connect said amplifier circuit means with said speaker circuit means and disconnect said d.c. supervisory power source from said speaker circuit means, second control means responsive to activation of said voice communication means for disabling said alarm signal generating means and connecting said voice communication means to said amplifier circuit means, detector means connected with the output of said amplifier circuit means, said amplifier circuit means including first and second alternate amplifiers and said detector means operating in response to loss of output signal from said first amplifier to disconnect the latter and connect said second amplifier in said amplifier circuit means and also to initiate a trouble indication, and third control means responsive to activation of said voice communication means for disabling said detector means.
 13. An alarm and emergency voice communication system as defined in claim 12 wherein said speaker circuit means includes a plurality of speakers connected in parallel, and capacitor means connected with said speakers for isolating said speakers from said d.c. supervisory signal while permitting normal operation of said speakers when said amplifier circuit means is connected with said speaker circuit means.
 14. An alarm and emergency voice communication system as defined in claim 12 wherein said alarm signal generating means includes first and second alarm signal generators, said first alarm signal generator normally being operatively connected with said first amplifier and said second alarm signal generator normally being operatively connected with said second amplifier, and wherein said second control means operates in response to activation of said voice communication means to disable said first and second alarm signal generators and operatively connect said voice communication means both to said first and second amplifiers.
 15. An alarm and emergency voice communication system comprising, in combination, alarm signal generating means, voice communication means, amplifier circuit means, speaker circuit means, said alarm signal generating means normally being connected with said amplifier circuit means, said speaker circuit means normally being disconnected from said amplifier circuit means, and said voice communication means when activated being connected with said amplifier circuit means, first control means responsive to initiation of an alarm for operatively connecting said amplifier circuit means and speaker circuit means thereby causing an alarm signal to be conducted to said speaker circuit, and second control means responsive to activation of said voice communication means and connected in overriding relation to said first control means for disabling said alarm signal generating means and operatively connecting said voice communication means with said amplifier circuit and speaker circuit thereby enabling voice signals to be conducted to said speaker circuit.
 16. An alarm and emergency voice communication system as defined in claim 15 wherein said alarm signal generating means includes first and second alarm signal generators and said amplifier circuit means includes first and second alternate amplifiers, said first control means operatively connecting said first alarm signal generator with said first amplifier and said second alarm signal generator with said second amplifier, and said second controL means operatively connecting said voice communication means with both said first and second amplifiers.
 17. An alarm and emergency voice communication system as defined in claim 16 wherein said first amplifier is normally connected in said speaker circuit means and said second amplifier is disconnected, and detector means responsive to a loss of output signal from said first amplifier for disconnecting the latter and connecting said second amplifier in said amplifier circuit means, and third control means responsive to activation of said voice communication means for disabling said detector means.
 18. In an alarm and emergency voice communication system of the type having alarm signal generating means, voice communication means, amplifier circuit means and speaker circuit means, an improved d.c. supervisory circuit for detecting both an open and a shorted speaker circuit comprising, in combination, a d.c. supervisory circuit including a d.c. power source connected with a speaker circuit to be supervised, first voltage sensing means which blocks voltage signals less than a first predetermined voltage while conducting higher voltage signals, second voltage sensing means which blocks voltage signals less than a second predetermined voltage while conducting higher voltage signals, circuit means interconnecting said first and second voltage sensing means, means in said supervisory circuit operable in the absence of an open or shorted circuit for producing at said circuit means a normal voltage intermediate said first and second predetermined voltage whereby said normal voltage is blocked by said first sensing means and conducted by said second sensing means, first trouble circuit means connected with said first voltage sensing means for producing a trouble signal in response to a voltage signal conducted past said first voltage sensing means in the event of an open speaker circuit, and second trouble circuit means connected with said second voltage sensing means for producing a trouble signal in response to blockage of a voltage signal by said second voltage sensing means when a short occurs in said speaker circuit. 